1. Field of the Invention
The present invention relates to a composite display device which is formed of a plurality of display units, and relates to, for example, a display device for a vehicle capable of being used as display of a dashboard in a vehicle.
2. Description of the Related Art
For example, in the vehicle, in order to provide information necessary for driving or information illustrating a state of the vehicle to a driver, a meter unit in which various instruments are embedded is built in a dash board in front of a driver seat. Various technologies related to a display device such as the meter unit have been developed than before so as to improve the visibility or the like.
For example, a head up display (HUD) having excellent visibility is already put into practice. Typically, the head up display projects an optical image to be displayed onto a surface of a combiner from an optical projection device. The driver can see an image which is reflected on the surface of the combiner. That is, display details of a display device that the driver can see is image-formed as a virtual image at an actually nonexistent position in front of the combiner. In addition, since the combiner partially transmits light, the driver can see an image such as actually existent scenery outside the vehicle in a state of being overlapped with the display details of the virtual image.
Techniques disclosed in JP-A-6-273690, JP-A-2000-214408 and JP-UM-A-63-96524 are known as the composite display device which is formed of the plurality of display units.
JP-A-6-273690 discloses a display technique relating to a game machine. Specifically, mobile information displayed on a display device 1 such as a CRT is reflected and diffracted by the hologram combiner 4 to form an image 5 which is enlarged and projected at distance. An observer can see the display where this image 5 and a movable or fixed display body 6 arranged at the rear of the hologram combiner 4 are synthesized. That is, the game machine disclosed in JP-A-6-273690 can perform the display in a state where the enlarged and projected image 5 at distance which is displayed as the virtual image and the display body 6 are synthesized. The enlarged and projected image 5 at distance corresponds to the background image of the game and the display body 6 corresponds to the contents of the game.
JP-A-2000-214408 discloses a picture display device capable of coping with the distance between the eyes of each individual and enabling an observer to surely view diffracted light with the right and left eyes. Specifically, an optical image is projected from picture display devices 1R and 1L, which are independently formed in the right and left sides, to a hologram combiner so that a video converged by the hologram combiner 3 is directly projected to the retina of an observer 4 and observed by the observer 4.
JP-UM-A-63-96524 discloses a head up display which causes a parallax to be generated between images reflected on the right and left eyes. Specifically, a symbol of the left eye and a symbol of the right eye are alternately output in time division. In addition, a light valve which alternately shields the light incident on the right and left eyes is provided.